Field of the Invention
The invention concerns a generator of current signals, more particularly such a generator that is capable of generating gating pulses of current of a high intensity (of the order of a few tens of amperes) regulated with great precision under a very high voltage of the order of several kilovolts. The invention is also directed towards a process for implementing such a generator.
Description of the Related Art
In certain applications—such as electrolysis, sterilization, the preparation of plasmas under vacuum, or for carrying out tests aiming to determine certain physical constants of homogeneous or inhomogeneous materials, such as, for example, their conductivity or their dielectric and/or inductive constants—it is sometimes necessary to apply voltages or calibrated currents through said materials, with predetermined periods of application of these currents or voltages.
Thus it may be useful in certain cases to apply to the terminals of a load—constituted, for example, by two electrodes inserted at a distance from one another in the material to be measured—current signals in the form of gating pulses of alternating polarity separated by so-called periods of relaxation during which no voltage and no current is applied. Ordinarily, use is made of a simple temporal sequence, in which a gating pulse of positive voltage of a few seconds is applied to the terminals of the load, then a period of relaxation of the same duration, followed by a gating pulse of negative voltage of the same duration, itself followed by a second period of relaxation.
By applying such a signal between two current-injection electrodes which are fixed in the material, certain characteristics of which it is desired to measure, and by measuring a resultant signal between two other measuring electrodes which are placed, for example, between the two injection electrodes, the resistivity and the dielectric constant of the material can be determined by comparing the shapes of the injected signal and of the measured signal.
For the precision of the measurements it is necessary to regulate the current applied during the positive or negative gating pulses, or even to inject this signal in the form of gating pulses of current, the voltage then adapting itself continuously, depending on the current to be obtained. In addition, it is essential that the gating pulses of current exhibit temporal characteristics (for example, concerning the rise-time of the edges of the signals) that are as effective as possible in order to enable a comparison without bias between the injected signal and the measured signal.
Generators are known that are used, for example, in the applications cited above or for the study of soils within the scope of the construction of buildings or of civil-engineering structures, or for the measurement of the moisture content in soils or in silos for storage of pulverulent materials. However, the known generators are suitable for measurements within a reduced operating range and develop voltages limited to a few hundred volts and a few hundred milliamperes.
A need therefore remains for a generator enabling high-tension signals, of the order of several kilovolts, to be provided, said signals being capable of causing a current to flow amounting to a few tens of amperes with a precision of less than one percent, in order to improve the performance of the known generators and to enable measurements to be performed on materials exhibiting high and/or highly variable impedance values.